Buggy code:
public final class FormInputModel implements IClusterable { public final class Line implements IClusterable { private String text ; public Line ( String text ) { } public String getText ( ) { } public void setText ( String text ) { } @ Override public String toString ( ) { return text ; } } private Boolean booleanProperty ; private Double doubleProperty = 20.5 ; private Integer integerInRangeProperty = 50 ; private Integer integerProperty = 100 ; private List < FormInputModel . Line > lines = new ArrayList < FormInputModel . Line > ( ) ; private Integer multiply = 0 ; private String numberRadioChoice = NUMBERS . get ( 0 ) ; private final List < String > numbersCheckGroup = new ArrayList < String > ( ) ; private String numbersGroup ; private UsPhoneNumber phoneNumberUS = new UsPhoneNumber ( "(123)<seq2seq4repair_space>456-1234" ) ; private Set < String > siteSelection = new HashSet < String > ( ) ; private String stringProperty = "test" ; private URL urlProperty ; public FormInputModel ( ) { } public Boolean getBooleanProperty ( ) { } public Double getDoubleProperty ( ) { } public Integer getIntegerInRangeProperty ( ) { } public Integer getIntegerProperty ( ) { } public List < FormInputModel . Line > getLines ( ) { } public Integer getMultiply ( ) { } public String getNumberRadioChoice ( ) { } public List < String > getNumbersCheckGroup ( ) { } public String getNumbersGroup ( ) { } public UsPhoneNumber getPhoneNumberUS ( ) { } public Set < String > getSiteSelection ( ) { } public String getStringProperty ( ) { } public URL getUrlProperty ( ) { } public void setBooleanProperty ( Boolean booleanProperty ) { } public void setDoubleProperty ( Double doubleProperty ) { } public void setIntegerInRangeProperty ( Integer integerInRangeProperty ) { } public void setIntegerProperty ( Integer integerProperty ) { } public void setLines ( List < FormInputModel . Line > lines ) { } public void setMultiply ( Integer multiply ) { } public void setNumberRadioChoice ( String favoriteColor ) { } public void setNumbersGroup ( String group ) { } public void setPhoneNumberUS ( UsPhoneNumber phoneNumberUS ) { } public void setSiteSelection ( Set < String > selectedSites ) { } public void setStringProperty ( String stringProperty ) { } public void setUrlProperty ( URL urlProperty ) { } @ Override public String toString ( ) { <START_BUG> StringBuffer b = new StringBuffer ( ) ; <END_BUG> b . append ( "[TestInputObject<seq2seq4repair_space>stringProperty<seq2seq4repair_space>=<seq2seq4repair_space>'" ) . append ( stringProperty ) . append ( "',<seq2seq4repair_space>integerProperty<seq2seq4repair_space>=<seq2seq4repair_space>" ) . append ( integerProperty ) . append ( ",<seq2seq4repair_space>doubleProperty<seq2seq4repair_space>=<seq2seq4repair_space>" ) . append ( doubleProperty ) . append ( ",<seq2seq4repair_space>booleanProperty<seq2seq4repair_space>=<seq2seq4repair_space>" ) . append ( booleanProperty ) . append ( ",<seq2seq4repair_space>integerInRangeProperty<seq2seq4repair_space>=<seq2seq4repair_space>" ) . append ( integerInRangeProperty ) . append ( ",<seq2seq4repair_space>urlProperty<seq2seq4repair_space>=<seq2seq4repair_space>" ) . append ( urlProperty ) . append ( ",<seq2seq4repair_space>phoneNumberUS<seq2seq4repair_space>=<seq2seq4repair_space>" ) . append ( phoneNumberUS ) . append ( ",<seq2seq4repair_space>numberRadioChoice<seq2seq4repair_space>=<seq2seq4repair_space>" ) . append ( numberRadioChoice ) . append ( ",<seq2seq4repair_space>numbersCheckgroup<seq2seq4repair_space>" ) . append ( numbersCheckGroup ) . append ( ",<seq2seq4repair_space>numberRadioGroup=<seq2seq4repair_space>" ) . append ( numbersGroup ) ; b . append ( ",<seq2seq4repair_space>selected<seq2seq4repair_space>sites<seq2seq4repair_space>{" ) ; for ( Iterator < String > i = siteSelection . iterator ( ) ; i . hasNext ( ) ; ) { b . append ( i . next ( ) ) ; if ( i . hasNext ( ) ) { b . append ( "," ) ; } } b . append ( "]" ) ; b . append ( ",<seq2seq4repair_space>lines<seq2seq4repair_space>[" ) ; for ( Iterator < FormInputModel . Line > i = lines . iterator ( ) ; i . hasNext ( ) ; ) { b . append ( i . next ( ) ) ; if ( i . hasNext ( ) ) { b . append ( ",<seq2seq4repair_space>" ) ; } } b . append ( "]" ) ; b . append ( "]" ) ; return b . toString ( ) ; } }

Fix:
StringBuilder b = new StringBuilder ( ) ;